Check the unit of an enthalpy change; either it is in kJ or kJ mol-1.
When calculating molar enthalpy change do not use the mass of the water/surroundings to calculate the number of moles. Also make sure you clearly state the sign i.e + or -.
When calculating free energy you should have enthalpy and entropy in the same units either both in kJ or both in J; temperature should be in K.
Make sure the state symbols are (g) in your equations defining ionization energy, electron affinity and bond enthalpy.
Bond enthalpy is for 1 mole of covalent bonds in gaseous molecules to form gaseous atoms.
Bond enthalpy is also an AVERAGE
Calculating enthalpy change using bond enthalpies is reactants - products as is using enthalpies of combustion; other are products - reactants.
Topic notes
Investigations
Prescribed investigationsOther investigations
Analysis
Resources
Worksheets
Calculating enthalpy changes
Hess Law
Below are the answers to all/most questions on the three exercise sheets above
Bond enthalpies
Standard enthalpy of formation and combustion
Born Haber cycles
Tutorials
flow of heat: this one also helps understanding bondingLike this one because it also links it to bonding and kinetic theory: heating curves
Some animations on calorimeters: calorimeter1 calorimeter2
Calorimetry experimentsCalorimetry experiment simulations
Hess's law calculations
Tutorial Hess's law
BBC test bite on Hess's law
bond enthalpies
Entropy Gibbs free energy from a biology perspective: Gibbs free energy in biology
Extension: an animation showing enthalpy changes when an ionic substance dissolves: dissolution of ammonium nitrate
BBC bitesize enthalpy of solution
Data sheet
Organic compounds thermodynamic dataRevision
Remember: